Question

Assertion (A): Aromatic primary amines can be prepared by Gabriel Phthalimide synthesis.
Reason (R): Aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Gabriel Phthalimide synthesis works ONLY for aliphatic primary amines, never for aromatic amines.

Answer 1

The Correct Option is D

Step 1: Concept
The Gabriel Phthalimide synthesis is a specific method for preparing pure aliphatic primary amines.

Step 2: Meaning
The key step in this synthesis is an $S_N2$ nucleophilic substitution where a phthalimide anion attacks an alkyl halide.

Step 3: Analysis
To prepare an aromatic primary amine (such as aniline), an aryl halide (such as chlorobenzene) would be required. However, aryl halides are extremely unreactive toward nucleophilic substitution because the carbon--halogen bond possesses partial double-bond character due to resonance. Therefore, the phthalimide anion cannot displace the halide ion.

• The Gabriel phthalimide synthesis is commonly used for the preparation of primary

aliphatic amines.

• In this method, the phthalimide anion acts as a nucleophile and attacks an alkyl halide through an \[ S_N2 \] mechanism.

• However, this method cannot be used to prepare aromatic primary amines such as aniline.

• Aromatic halides (aryl halides) like chlorobenzene are highly resistant to nucleophilic substitution.

• One important reason is resonance between the halogen atom and the benzene ring.

• The lone pair of electrons on the halogen overlaps with the $\pi$-electron cloud of the benzene ring, giving the carbon--halogen bond partial double-bond character.

• Consequently, the C--Cl bond becomes shorter and much stronger than that in alkyl halides.

• Moreover, the carbon atom bonded to chlorine is \[ sp^2 \] hybridized, making the bond even stronger.

• Therefore, the phthalimide anion cannot replace the halide ion, and the Gabriel synthesis is unsuitable for preparing aromatic primary amines.

Step 4: Conclusion
Aromatic primary amines cannot be prepared this way, making the Assertion false. The Reason provides the correct chemical justification for why the reaction fails.

Final Answer: (D)